Date on Master's Thesis/Doctoral Dissertation

5-2011

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Chemical Engineering

Committee Chair

Berson, Robert E. (Eric)

Subject

Biomass conversion--Research; Ethanol

Abstract

Enzymatic hydrolysis is an important, but time limiting step in the process of converting biomass into ethanol. High solids concentrations are desired in order to minimize reactor size and achieve a higher concentration of glucose in the end product stream. However, higher solids concentrations lead to higher viscosities and hence, mixing and mass transfer becomes more difficult. In this study, a mixer designed to overcome the mass transfer limitations was used to conduct enzymatic hydrolysis of dilute-base pretreated corn stover, wheat, and miscanthus at high solids concentrations. This was done to determine if overcoming the mass transfer limitations would improve glucose release rates and yields, as was the case in a previous study on dilute acid pretreated corn stover. Solids concentrations were tested at 20%, 25%, and 30% for each substrate. The glucose yields during mixer trials were higher for lower solids concentrations for all three substrates, contradicting the previous results which showed that glucose release rates and yields were maintained as solids content increased in the mixer. The 20% solids corn stover released 70% more glucose than the 30% solids did. Yields for 20% solids were in the 60% range, which is low but close to the expected range. For wheat, 400% more glucose was released for 20% solids than 30% solids. Yields for 20% wheat solids were in the mid 60% range, which is also close to the expected range. For miscanthus, the increase was 36%. Yield for 20% miscanthus solids was below 40%, which was on the order of untreated sawdust in a previous study and indicates an ineffective pretreatment method for this substrate. The contradictory results indicate there may be some effect other than mass transfer limitations that affects glucose release rates and yields. The slurries tested had much larger particle sizes and lacked the free water which gives the consistency seen with other pretreatment methods. This is most likely due to poor pretreatment. Due to the consistency, it was difficult to measure viscosity and, hence, determine if mass transfer limitations were overcome in these slurries.

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